High resolution modelling of fate and transport of organic micropollutants and their effect on ecosystems in small rivers

The PhD project aims at creating a better understanding of the dynamics of concentrations, fate and transport of organic micropollutants and their effects on ecosystems in small rivers. In the UK, much effort has been put by the Environment Agency and the water industry in developing a comprehensive source apportionment model for chemicals emissions (SAGIS-SIMCAT) on a national scale. In this project, we will focus on mathematical modelling of hydrological and environmental processes in the small rivers. Small rivers are highly dynamic systems in which water flows and emission loads can change orders of magnitude in a short time. Current water quality models are based on simple dilution and first order decay models to describe environmental processes in a steady state approximation. Therefore, existing models are inadequate for small rivers. Building on the accurate emissions and source apportionment data, we will – for the first time – develop a water quality model for small rivers to describe pollutant concentrations and loads in a high spatial and temporal resolution. The model will be used to quantify environmental risks, the effects for ecosystems, and help decision makers in prioritising abatement options.

In the recent years, the presence of organic micropollutants in river waters, including pharmaceuticals and personal care products (PPCPs), their transformation products and many pesticides, has been confirmed up to several tens of micrograms per litre. Although it is believed that presence of pharmaceuticals is not directly harmful for humans, there is strong evidence that these concentrations are harmful for aquatic life. For the UK, a national comprehensive source apportionment model has been developed (SAGIS), but the fate and behaviour in small dynamic river systems has never been accurately described.

PPCPs are mainly discharged into the surface water via sewage treat¬ment works. Pesticides, like metaldehyde, and nutrients will reach the river water via diffuse pathways. During river transport, concentrations generally will reduce further by dilution and other attenuation effects, e.g. adsorption to sediments, biodegradation, and photochemical degradation by sunlight. Most water quality models apply simple first order decay kinetics in a steady state approximation aiming at larger river systems such as the Rhine, but inadequate for small rivers. In our approach, we will develop a river model that couples hydrological and water quality modelling at high spatial and temporal resolution.
The model will be used to perform a time and location dependant risk assess¬ment of different functions of the surface water and its riparian areas. This will enable new risk evaluation methodologies for specific functions along the river. The model will also enable scenario studies to predict the effects of abatement options, like additional treatment steps for removal of pharmaceuticals at STWs.

The student experience will comprise a combination of cutting edge modelling of hydrological and (bio)chemical processes in rivers. The project will include fieldwork for advanced sampling required to validate the models. Furthermore, the student will be working in close collaboration with Wessex Water and the Environment Agency, aiming at integration with the SAGIS system.

The studentship has the following objectives
1. To deliver a time-dependent hydrological and water quality model for a small-scale river
The model will be based on dynamic hydrological models that will be expanded with a water quality model, incorporating (bio)chemical degradation and adsorption processes. We will use the Bristol Avon as a test base and use emission data from SAGIS. Also, integration of the model in the SAGIS-SIMCAT modelling systems will be investigated.
2. To calibrate and validate the model for key PPCPs and pesticides
A monitoring campaign will be setup to collect biological and chemical data for calibrating and validating the model. Model compounds will be selected for independent validation of the different (bio)degradation and attenuation pathways.
3. Develop a risk assessment methodology
This objective will use the model to setup a risk assessment methodology and identify risks for specific ecosystem functions such as supporting habitats, waste treatment and assimilation, biological control, and water supply. The applicability of the model as a decision support tool will be tested.